svn commit: r349233 - head/sys/sys

Bruce Evans brde at optusnet.com.au
Thu Jun 20 18:44:30 UTC 2019


On Thu, 20 Jun 2019, Alan Somers wrote:

> On Thu, Jun 20, 2019 at 10:43 AM Bruce Evans <brde at optusnet.com.au> wrote:
>> Summary: <sys/ioctl.h> and the headers that it includes should declare
>> minimal types to compile (so __int64_t is enough).  Most uses of this
>> header require including domain-specific headers which declare the
>> relevant data structures.
>
> Bruce, would you be satisfied by switching from <sys/types.h> to
> <sys/_types.h> and from int64_t to __int64_t?

Not quite.  The kernel block number type is daddr_t, and [__]int64_t is
a hard coding of that.  Hard-coding of typedefs is good for reducing
namespace pollution, but it is not done for the nearby use of off_t.

Unfortunately, daddr_t is only declared in <sys/types.h>.

The type daddr_t seems to be correct, but ffs conflates it with
ufs2_daddr_t.  It is only for blocks of size DEV_BSIZE, while fs blocks
are usually larger.  The conflation is just a style bug because 64 bits
should be large enough for anyone and ffs does the necessary conversions
between DEV_BSIZE-blocks and fs-blocks.

ext2fs seems to be more broken in this area.  It doesn't have
ext2fs_daddr_t, but hard-codes this as int32_t or int64_t.  int32_t
became very broken when ext2fs started attempting to support unsigned
block numbers.  Now, ext2_bmap() corrupts "daddr_t a_bn" to "int32_t
bn" when it calls ext4_bmapext().  This has a chance of working via
unsign-extension bugs provided a_bn fits in uint64_t.  It is sure to
fit for a valid a_bn, but perhaps your new ioctl allows probing for
panics using invalid a_bn.  ext2_bmap() also calls ext2_bmaparray().
That used to have essentially the same style bugs as ffs (with the
ext2fs type corresponding to ufs2_daddr_t spelled int32_t), but it now
correctly uses daddr_t.  Internally, it misuses daddr_t for ext2fs
block numbers, and there is an ext2fs block number type after all
(e2fs_lbn_t = int64_t) which it uses only for metalbn.

It looks like the older ext2fs code was fixed, especially if older ext2fs
is limited to int32_t block numbers, but the ext4 case is quite broken
since unsign extension bugs don't help it.  a_bn starts as int64_t, then
is truncated to the function arg "int32_t bn", then the function assigns bn
to "int64_t lbn" and doesn't use bn again.

Using a generic int64_t type in all interfaces would avoid some of these
bugs, so I don't mind using it for the API.  Just add a note that it must
be large enough to represent all useful values of daddr_t.

Bruce


More information about the svn-src-head mailing list